Indecent
by iinoyb
Summary: Sans interrupts Papyrus during some alone time. The results are highly unexpected. (NSFW, Swap Sans/Swap Papyrus)


**Warnings:** Swapcest (Swap Papyrus/Swap Sans), Sex, Incest, ecto-biology

* * *

Papyrus listened closely once again, but the house was still utterly quiet. His brother must still be out human-hunting, as is expected of a responsible sentry.

He closed his door just in case.

With a sigh the tall skeleton sat back on his dingy mattress, pushing the bundled up pile of blankets to the floor unceremoniously. His usual hoodie had already been discarded earlier, draped over the back of his desk chair, leaving him with just his shorts and T-shirt on.

After a deep breath, he allowed his head to fall back to rest against the wall, moving his hand under the garment to grasp at sensitive ribs, rubbing them slowly but deliberately.

He had done this countless times before, Papyrus knew exactly where to touch or stroke to get the magic inside him to stir, his soul fluttering ever so slightly in his rib cage.

It was almost a necessity. With somebody like Sans as a brother, he didn't get nearly as much 'alone-time' as he might have wanted, and it was important to make the most of the chances he did get to entertain himself.

It was either that, or find someone to lend him a hand.

Somehow the notion had lost most of it's savor lately, and Papyrus knew exactly why.

His eye sockets slipped close as the rubbing sped up, small sounds escaping his mouth at the delectable sensation.

Like this, he could almost imagine it were not his own hands invading his body, but rather those of his innocent brother.

The mere thought made his face flush, orange tinge heating up the pale-white bones.

He really shouldn't harbor thoughts like this, an insistent voice inside his head was saying. It was wrong. It was sinful. It was positively immoral.

It was hard to heed that voice when the sensations running through him were making him gasp, despite the lack of lungs, and his other hand was busy slipping down the front of his pants to lightly grasp the member his magic had ever so helpfully provided him.

As he pumped the length slowly, a practiced rhythm meant to bring him to completion with relative ease, Papyrus could not help let the fantasy escalate a slightly bit further.

He wondered how Sans would touch him. All hesitation and uncertainty, those deft phalanges slowly probing and prodding at his bones to see which spots would make him gasp and writhe in pleasure.

There wasn't a doubt in his mind his small sibling would be utterly thorough in his explorations. The great Sans never did anything by halves.

He indulged in imagining what he could do to Sans in return. The faces he would make, or the sound of half-whispered pleas for more.

The mere thought of those beautiful blue eyes half-lidded in aroused ecstasy was enough to make Papyrus pant harder, picking up the speed and adding a small twist of the wrist for good measure.

The room was filled by the sound of his harsh breaths and the slick slide of precum as it gathered on his fingers and rubbed along his girth.

Maybe Sans would even allow him to go further, allow Papyrus to show him what else their magic can accomplish once you _really_ get in the mood.

Maybe they could-

"Papyrus?"

All thoughts came to a screeching halt at the sound of that voice uttered from his doorway.

His eye sockets shot open immediately and the tall skeleton felt the heat in his face get twice as intense at the sight of just the person he had been fantasizing so hard about, looking at him.

That look gave Papyrus pause. It wasn't disturbed, or disgusted, as he had expected it to be. Sans didn't even look confused or embarrassed.

Rather, his face held a certain degree of curiosity. And was that amusement?

"What are you doing?" the younger brother asked innocently, the tiniest smile grazing his lips.

The question spurred Papyrus's brain back into action, blatantly realizing he was still sitting there completely exposed, with one hand up his shirt and the other on his rock-hard dick.

Which had not deflated at the least by the unexpected interruption, may he add. Quite the opposite, even.

"S-Sans? What are you doing here, weren't you supposed to be out until evening?" The taller managed to splutter, trying to close his legs but finding himself terribly inconvenienced by his shorts, which had slipped down and now tangled around his knees.

His face must have been the same color as a carrot by now, and he cursed himself for discarding his blankets so stupidly earlier, as he scrambled to cover his indecency.

Sans seemed unperturbed. Or was he? As the smaller made his way into the room, Papyrus could almost swear there was a slightly blue tinge to his siblings face also.

There was barely 3 feet separating the two now, and Papyrus found himself desperately wishing his stupid erection would flag already.

"I was." Sans confirmed, entirely too close for comfort now. "But I forgot my scarf."

The older brother blinked, noticing that, upon closer inspection, Sans was indeed without the trademark garment. He was also definitely blushing, Papyrus noted.

The mattress dipped slightly when Sans dropped one knee onto it, getting even closer, making Papyrus press backwards. Too bad he was already flush against the wall.

"Imagine my surprise when I instead find the entire house filled with excited magic. Your magic."

Damn it! Papyrus could dust himself right now. He wasn't usually so complacent when it came to reeling in his magic, but the forbidden fantasies he had been indulging in had thoroughly messed up his concentration.

Maybe he should start believing in karma already.

Sans was positively in his face now, and it was taking his nonexistent breath away. The insistent voice in the back of his head was back, saying he should probably scramble away with whatever remained of his dignity, but something kept him rooted to the spot.

"I-I-I-" Was all he managed to stutter, so he allowed his slack jaw to snap shut instead.

Sans bend down slowly, bringing his mouth right beside his brother's ear hole, and his voice became almost sultry as he whispered.

"This is exactly why I always bug you to train with me, Pappy. Such an embarrassing slip of control."

And then those small hands that plagued his wildest dreams really were on his cock, stroking up and down slowly but with determination.

Papyrus's hands came up to grasp his brother's shoulders, skull thudding against the wall again, and Sans stopped for the tiniest of moments, gauging if his brother was attempting to push him away.

Instead, Papyrus pulled him in, clacking their mouths together almost painfully in the skeleton equivalent of a kiss. Sans pressed even closer, now practically sitting on his brothers lap, long legs straddled underneath him.

The stroking resumed, and Papyrus gasped and moaned in pleasure, marveling at how the same touches he was applying to himself earlier could feel so much better now that it was his brother wrecking him.

Using Sans shoulders as leverage, the tall skeleton began grinding his hips forward, feeling his brother's still clothed member brush against his own.

The small huff the younger brother let out spurred him on, thrusting his pelvis slowly, hands now coming down to grasp the smaller hips, thumbs rubbing slow circles.

"Ah, Nh- S-Sans. I didn't kn-know you-" Papyrus managed shakily, feeling his brothers gloved hand rubbing his tip twice before resuming their previous motions.

"R-Really, Pappy." Sans was starting to sound slightly breathless himself. "I thought I mmmhn- made it obvious enough."

The smaller skeleton was pushing their pelvis's together now too, more insistently than Papyrus would have expected of him.

Papyrus wasn't entirely sure what those words meant, but he could think about it some other time.

When he wasn't busy desperately rutting into his apparently not-so-innocent brother, barely able to bring out an articulate sound.

When Sans's movements stopped, Papyrus managed to pry his eyes open again (not remembering having closed them in the first place), only to see Sans observing his handy-work with that same amused expression from earlier on his face.

He brought his eyes up to meet his brother's face, and the purely predatory gaze in those orbs sent an involuntary shiver down Papyrus's spine.

"I think that's enough foreplay, don't you?" The younger said, the almost bubbly tone contrasting strongly with their current predicament.

Before Papyrus could so much as blink, Sans was removing his own pants, also pulling those of his brother further down his legs and out of the way for good measure.

Then, small hands began tugging on his pelvis, pulling it forward and making his back slide down the wall slightly.

"Ah- Bro, what are you-" As if he didn't know exactly what Sans was doing, as if it didn't send and excited tremor through his bones.

Sans looked at him, wide eyes open and pure as always. "Well, I'd say it's pretty obvious. I'm going to fuck you."

The sound that escaped his throat was embarrassing in how desperate it sounded, but there was already something pressing at his entrance, and Papyrus squeezed his eyes close again instead.

He gasped feebly at the sensation. It was hot and full and so much more than he expected.

Papyrus had experimented with that particular aspect of his magic manifestation before, but one or two fingers were nothing compared to the appendage pushing inside him now.

When he felt Sans's pelvis flush against his own, he managed to half-open his lids again, almost whimpering at the look of complete delight on his smaller sibling's face.

Sans was waiting for him to adjust, so Papyrus used the opportunity to grasp his brothers shoulders and pull him close for another kiss, utterly enjoying the feeling of being connected in the most literal sense of the word.

He wouldn't have minded staying like that for entirety, but Sans seemed to have other plans.

With a slow movement, the younger brother pulled out, until barely his tip was still inside, before thrusting back in hard.

Papyrus gasped loudly, not able to restrain the sounds trying to escape anymore when Sans set up a demanding rhythm.

The grip on his brother's shoulders became the only thing anchoring him as the world narrowed to the feeling of his magic contracting around that hard length and the stuttering of his soul in his chest.

It was utterly amazing, and judging by the choked groans above him, Sans would agree.

Sans shifted them slightly, reaching even deeper and hitting that certain spot inside Papyrus's pelvis which made him mewl loudly.

The small skeleton giggled as he made sure to aim true on every thrust, Papyrus now noisy enough to alert the whole Snowdin to their sinful conduct.

"Anh- If I had known you'd be so indecent I'd have brought my scarf. Would make a pretty decent gag, don't you think." Sans grunted, the slightly hazy look in his eyes betraying he wouldn't hold out much longer either.

He bent forward, thrusts picking up speed as he whispered in his elder brother's ear hole once more.

"Well, maybe next time."

And that did it. With a barely restrained scream, Papyrus came, cum shooting out and staining their shirts as magic burst in the air.

The added pressure around his member only spurred Sans on, practically fucking his brother into the mattress as the taller skeleton whimpered at the overstimulation.

After a few more thrusts, the younger brother climaxed also, making an utter mess of the inside of his brother's pelvis and rib cage.

It was a good look on him, Sans decided.

He collapsed on top of Papyrus, feeling those long arms envelop him and hold him close.

"That was...unexpected." the taller managed to huff out, after they had laid in the afterglow for a few minutes.

"Really, Pappy?" Sans giggled, and it was almost ridiculous how his voice could return to pure innocence so quickly. "I thought I made it obvious for weeks now. You're just too much of a lazybones to notice."

A small laugh escaped him, and Papyrus gave his younger sibling a wink. "Guess I was just too much of a _numbskull_ to notice."

Small fists thumped his chest, an irritated huff accompanying the gesture.

"I love you, bro." He wasn't sure what made him say it, but it felt right.

"Of course, I am the great Sans after all." Sans looked at him with a small smile, before burying his head against his taller brother's collarbone. "Love you too, Pappy."

They lay there in comfortable silence, and Papyrus was just starting to drift off, when he heard the smaller skeleton whisper in his ear again.

"Now, about that next time."

* * *

 **Three hoorays foe surprise Top!Berry**


End file.
